High Performance Concrete And Higher!

Dr. A. K. Mullick, Former Director General, NCBM

The concept of High Performance Concrete (HPC) as
something different from the ordinary, run-of-the mill
concrete was evolved nearly five decades ago. HPC was
designed to meet special requirements of strength, durability and
fluidity of individual projects, by choice of appropriate materials,
workmanship and quality control. In India, high performance
concrete has been widely adopted in Nuclear power generation,
infrastructure and water resources projects. Meanwhile,
development of concrete with greater characteristics, called
‘Ultra High Performance Concrete’ (UHPC) has been going on
in many countries. This paper summarises the trend and the
steps required to make wide application of UHPC in structural
engineering applications.High Performance Concrete
The advent of superplasticizers and silica fume are among
the foremost developments in concrete technology in the last
few decades; which led to high strength and high performance
concrete. Superplasticizers allowed the workability of concrete
to increase greatly, or to lower the water/cement ratio,
resulting in lower capillary porosity and high compressive
strength. Addition of silica fume aided high strength by
pozzolanic reaction and denser packing of solid particles by fine
powder effect. This resulted in higher compressive strength and
enhanced durability.
High performance concrete is defined as ‘Concrete, which
meets special performance requirements that cannot be always
achieved routinely by using only conventional materials and normal
mixing, placing and curing practices’. The requirements may
involve high strength; greater durability and increased service
life in severe environments; high ductility, toughness and blast
resistance etc. (1,2).
Another requirement can be very high workability without
segregation; this is the main characteristic of self-compacting
concrete (SCC).Basic Considerations
The basic considerations of high performance are the
relationships linking water-cement ratio to the strength and
durability of concrete. The requirements of high strength and low
permeability (high durability) are achieved by (3);
– Low water-cement ratio for high strength (Fig. 1),
– Low water-cement ratio for low permeability (Fig. 1),
– Pore blocking by fine powders
– Partial replacement of cement by silica fume, fly ash or slag
to reduce cement content
– Increased fine powder and low water content require the use
of superplasticizers.

Another aspect requiring attention is the brittle nature
of concrete. Concrete is a quasi-brittle material, prone to
cracking. The brittleness increases with high strength (Fig.3).
Another related development, therefore, is the use of fibre
reinforcement, to improve ductility, crack resistance and
toughness.

Necessary Ingredients
With the above information, it is easy to list the necessary
ingredients of high performance concrete. Cement, aggregates
and water are the usual ingredients of concrete; additionally, for
high performance concrete, the following is required (3);
– Silica Fume,
– Superplasticizers,
– Fly ash, Granulated Slag – optional,
– Viscosity modifying agents (VMA) for very high workability
concrete, self-compacting concrete (SCC).
– Fibre reinforcement for ductility, toughness, abrasion resistance.Typical Applications in India
High strength and high performance concretes have been
widely used in India during the last three decades for construction
of nuclear power projects, long span bridges, high-rise buildings
and water resources projects. As such, only a few illustrative
applications are mentioned below.
High strength concrete is used where strength is the
basic consideration, e.g. in buildings, industrial structures. It is
noteworthy that IS: 456 (draft revision) defines ‘High Strength
Concrete’ from Grades M65 to M100, but does not mention
high performance concrete. On the other hand, where durability
is added consideration, e.g. in river bridges, high performance
concrete is used. IRC Concrete Bridge Code IRC: 112 – 2011
defines ‘High Performance Concrete’ from Grades M30 to M90.
It should be kept in mind that high performance concrete is not
always the same thing as high strength concrete.
Among the application of high concrete strength, mention
may be made of JJ Flyover in Mumbai. The superstructure of the
viaduct used M75 Grade concrete, which was manufactured in
RMC plants (4).

Target compressive strength of concrete at 28 days was 83.2
MPa. The mix composition per m3 of concrete was as follows;
Cement - 500 kg
Silica Fume - 50 kg
Fine aggregate - 682 kg
Coarse aggregate - 1156 kg
Water - 148 litres (w/b ratio = 0.269)
Superplasticizer - 8.25 litres
Properties of concrete achieved in the field were;
Slump- 130 to 180 mm at RMC plant,
80 to 120mm at placement, after 150 minutes,
Field strength obtained was 79.6 MPa at 28 days (average) and
94 MPa at 365 days.
CoV - 2.64%.
Low variability was testimony to strict quality control
Coming to high performance concrete, domes of Reactor
buildings in nuclear power projects at Kaiga, Tarapur and RAPP
were among the first to use high performance concrete (5).
The performance characteristics required were; moderate
compressive and high tensile strength; very high durability; low
creep and shrinkage; low permeability and good workability.
Relatively crack-free performance was required to prevent
leakage of radioactivity.

Typical mix proportions (per m3 of concrete) were (Table 1)

The average 28–day compressive strength was 77 MPa, and
CoV was 5%. The cement content was reduced subsequently, as
experience was gained.
Most of the highway bridges use high performance concrete.
The mix proportions for M60 grade pile caps for Bandra – Worli
Sea link project are given in Table 2 below.

This project was among the earliest to use ternary blend
for binder system (OPC + fly ash + silica fume), now becoming
common. This practice of ternary cement blends allows optimum
packing of fine materials; a trend, which extends to all solid
materials including aggregates in further developments of high
performance concrete (6). It is to be noted that M60 Grade
concrete was achieved with 320 kg cement per m3.
In the Waterways Sector, high performance concrete is
used for locations subjected to abrasion and impact, e.g. intake;
overflow sections, sluices and stilling basins in spillways. M60
concrete is routinely specified for such applications (6). Another
area of application is for immediate and permanent roof support
for underground caverns like Powerhouse, Transformer Hall,
Desilting chambers and Sedimentation chambers, or for the lining
of tunnels, where fibre-reinforced shotcrete is used.Self-Compacting Concrete
Another type of high performance concrete is Self
Compacting Concrete (SCC). Self-Compacting Concrete is a
concrete that fills uniformly and completely every corner of
formwork by its own weight and fluidity without application
of any vibration, without segregation, whilst maintaining
homogeneity. It is suitable in situations where;
– Reinforcement is very congested,
– Access to allow vibration is not available,
– Complicated geometry of the formwork,
– Pouring is possible only from a single point,
– Speedy placement is required
It also has the advantage of no noise due to vibration and no
requirement of finishing.
Because of ease of placing, SCC is now widely used in many
constructions in India. Its applications started with concrete of
moderate strength grades (M35 or so), where congestion of
reinforcement or difficulty in placing were the primary reasons.
Its application to high strength concrete (M60 Grade) was
extended to bridge piers in Signature Bridge in Delhi (6), and
later on to many high-rise buildings, where M80 or M90 grade
concrete is being used (7).
In the absence of any Code for mix design, comprehensive
guidelines of EFNARC are widely used (8). It also prescribes
necessary tests for fluidity, passing ability and cohesiveness of
concrete and suggests appropriate values of test results for
different placing conditions.Further Developments - UHPC
With appropriate mix design, high strength and high
performance concretes of compressive strength approaching
100 MPa at 28 days became common, including in India.
Simultaneously, the development of very high strength concrete
following ‘Reactive powder concrete (RPC), Macro defect free
cement (MDF) or Dense silica particle cement (DSP) routes were
pursued. New generations of high efficiency superplasticizers
rendered high fluidity; and fibre reinforcement was used for
ductility and toughness. This led to the recent trend in many
countries to develop ultra high performance concrete (UHPC) and
their industrial applications. Compared to the common strength
level in HPC of around 60 - 100 MPa, the ultra high performance
concrete has strength levels of up to 200 MPa or more.
A common classification on the basis of compressive strength is
given below:
– High strength concrete (HSC) – 50 to 100 MPa,
– Very high strength concrete (VHSC) – 100 – 150 MPa,
– Ultra high strength concrete (UHSC) – 150 – 200 MPa, and
– Super high strength concrete (SHPC) – 200 – 250 MPa.
As mentioned above, these are achieved by with the use
of improved materials, very high amount of cement and silica
fume, (called ‘reactive powders’), low water/binder ratio of the
order of 0.11 – 0.22 made possible by the use of higher dosage
of high efficiency superplasticizers. Addition of fibres results in
high flexural strength and improved ductility. Conventional sized
coarse and fine aggregates are omitted. Some of the formulations
are commercially available in trade names of DUCTAL or
CERACEM.
Reactive Powder Concrete (RPC) Ductal– High cement
content @@ 1000 kg/m3, silica fume – 230 kg/m3 and water
binder ratio – 0.11 – 0.15, Steel fibres @@ 200 kg/m3 are added
to render ductility. RPC does not contain coarse aggregate
and maximum size of fine aggregate is 0.4 – 0.6 mm. Typical
compressive strengths of 170 – 230 MPa or higher have been
obtained.
Special Industrial Concrete (BSI) Ceracem – Mix proportions
are similar to Ductal, except fine aggregate of size up to 6 mm
are used. Typical strength levels are 150 – 175 MPa.
ACI Committee 239 has given definition for Ultra High
Performance Concrete (UHPC) as ‘Concrete that has minimum
specified compressive strength of 150 MPa with specified
durability, tensile ductility and toughness requirements; fibres are
generally included to achieve specified requirements’ (9).
Early Applications
A recent (October 2015) Symposium on ‘Ultra High
Performance Concrete’ held in Kolkata contains state-of–theart
information on development, applications and challenges
on the use of UHPC (10). Much of the information given below
is gathered from the above publication, which lists pioneering
applications of UHPC as:
– 130 MPa UHPC for an 88 story building in Chicago (1987),
– 300 MPa UHPC used for 60m long Sherbrook bridge in
Canada (1997), and
– 200 MPa UHPC used for 120 m long pedestrian bridge in
Seoul, South Korea (2002).
Sherbrooke Bridge (Fig. 6) has a 60 m clear span, 3.3 m wide.
It was constructed with six precast UHPC elements. The precast
elements were 3-dimensional space truss, which were posttensioned
at the site. 300 MPa Ductal concrete was used. It is
used as a footbridge.

Bridge of Peace in Seoul, South Korea (Fig. 7) has a 120 m
span, The structure consists of six precast units made with 200
MPa Ductal. In longitudinal directions, the segments are posttensioned
by six tendons. In transverse direction, single strands
are used along with small, specially produced anchors.

Opportunities And Challenges On Large Scale Application:
Ultra high performance concrete not only offers extremely
high compressive strength, but outstanding durability. Extremely
high compressive strength of concrete will allow a high
degree of precompression and high level of tensile stresses
can be compensated (10). Addition of fibres provides major
enhancements of ductility and tensile capacity. The most notable
characteristic is extremely dense microstructure of the matrix
due to the high amount of fines with an optimum packing density
and low water/binder ratio. Consequently, long span structures or
very high buildings with reinforced and prestressed concrete are
potential areas of application.
However, the wide scale application has been restricted due
to the fact that UHPC-specific structural design rules are not
available (9, 13). Framing of design rules and testing standards
have been identified as a major task for ASTM and ACI (9).
All the earlier applications were designed with conservative
approaches, fully prototyped, and load tested to failure. In the
early implementation of such break-through technology, the risks
of owner, designer, concrete suppliers and contractors add to the
costs. (13). Reference 10 gives a good insight into the current
research activities on material- and structural design aspects
being carried out in Europe, USA and some Asian countries like
South Korea and China.
Ultra High Performance Fibre-Reinforced
Concrete (UHPFRC)
Meanwhile, more applications are reported for repair and
capacity enhancement of existing concrete structures, which
require high strength, improved durability and multiple fine
cracking phenomena. The latter property is owing to ‘strainhardening’
nature of the composite. Such a composite will have
very high tensile strain capacity; about 4 per cent i.e. 400 times
that in normal concrete.

The concept of strain-hardening is explained in Figure 8
(14). In conventional FRC, peak stress will be followed by a
falling softening branch, with not much increase in tensile
strain and opening of large crack (Fig. 8 (a)). On the other
hand, the stress-strain curve of a strain-hardening composite
starts with a steep initial ascending portion up to first structural
cracking (Fig. 8 (b) - part I), followed by a strain-hardening
branch where multiple micro cracks develop (part II) (14). The
peak point at the end of strain-hardening branch, B in Fig. 8(b)
corresponds to the maximum post-cracking stress and strain.
At the peak point, one crack becomes critical; onset of crack
localization takes place, and decrease in the resistance (Fig. 8
(b) - part III). Multiple crack formation, of 50 µ to 70 µ width,
rather than a single crack, is important for strain-hardening
response.
Applications in Repair and Strengthening
Pioneering applications of UHPC for strengthening and repair
of structural members are reported in Ref. 15. Typical examples
include;
– Widening of existing bridge (Figure 9).
– UHPFRC protection to a crash barrier wall.
– Rehabilitation of bridge pier using precast UHPFRC shell
elements (Fig. 10), and
– Strengthening an industrial floor.

Typical composition of UHPC in such applications will be as
given in Table 3 (10, 15).
Table 3. Typical composition of UHPC for repair applications

Fine powders are batched premixed, which are then mixed
with the rest in a high shear mixer. The mixing can be at the site or
transported after mixing in a central plant (13). The workability
is high; around 200 mm slump. After 24 hours curing at room
temperature, the mix may have to be steam-cured at 90OC for
48 to 72 hours. In such cases, precast elements are used. The
design compressive strength is 180 MPa and design tensile
strength 13.0 MPa.Indian Efforts
The use of strain-hardening, ductile concrete of normal
strength grades (M40 or M50) have been proposed for joint
less bridge decks in NHAI project. Because of high tensile strain
capacity and controlled crack behaviour, expansion joints are
proposed to be eliminated. Full details are in Ref. 16. This is in line
with what is practised in the USA.
IIT’s and SERC Chennai have reported investigations on
high and ultra-high performance fibre-reinforced concretes. In
SERC investigations, the 28 – days compressive strength of the
composites ranged from 81MPa (high performance concrete) to
188 MPa (Reactive powder concrete). Uses of different types of
fibres – both steel and polymer, like PVA or PP, to obtain strainhardening
behaviour has been investigated by different academic
institutions. Use of UHPC overlay for repair of damaged RCC
beams have been reported from SERC Chennai.
It is apparent that the design and construction of high-rise
structures or long span bridges with UHPC will have to wait, till
design rules are framed abroad and then in India. Enterprising
engineers can opt for innovative designs on the basis of prototype
testing. However, use of UHPC for repair, strengthening and
retrofitting applications can start straight away.
(Dr. A. K. Mullick, the former Director General of National Council
for Cement and Building Materials in India, has spent more than
45 years in research, teaching, design and consultancy, devoted to
propagation of sustainable concrete practices. He has authored 170
papers, two book chapters and is the co-inventor of six patents.)
References
1. Strategic Highway Research Program, SHRP-C/FR-91-103,
High Performance Concretes: A State-of-the-Art Report,
1991, NRC, Washington D.C., p. 233.
2. Neville, A.M., ‘Properties of Concrete’, 4th ed., Pearson
Education Asia, Essex, England, Indian Reprint, 2000.
3. Mullick, A.K., High Performance Concrete in India –
Development, Practices and Standardisation, Journal, Indian
Concrete Institute (ICI), Vol. 6 (2), 2005, pp. 7 – 14.
4. Saini, S., Dhuri, S. S., Kanhere, D.K. and Momin, S. S., High
Performance Concrete for an Urban Viaduct in Mumbai,
Indian Concrete Journal, October 2001, pp. 634-640.
5. Basu, P.C., NPP Containment Structures: Indian Experience in
Silica Fume based HPC, ibid, pp. 656-664.
6. Mullick, A. K., ‘Sustainable binder combinations for durable
infrastructure Projects’, Proceedings., 3rd Asian Conference
on ‘Ecstasy in Concrete’, ACECON 2010, Indian Concrete
Institute, Chennai, December, 2010, pp. 395 – 404.
7. Reddi, S., A., ‘Self compacting concrete for the tallest
building in India’, ibid, 815 – 826.
8. European Federation for Specialist Construction Chemicals
and Concrete Systems (EFNARC), The European Guidelines
for Self Compacting Concrete; Specification, Production and
Use, May 2005, 63 p. Website - www.efnarc.org.
9. Ahlborn, Theresa M., Advancing UHPC in the United States
concrete construction market, 4th Asian Conference on
‘Ecstasy in Concrete’, ACECON 2015, Indian Concrete
Institute, Kolkata, October, 2015, pp. 1 - 8.
10. Proceedings of the 1st International Symposium of Asian
Concrete Federation on ’Ultra High Performance Concrete,
(ACF 2015), October, 2015, Kolkata, Indian Concrete
Institute, 107p.
11. Aitcin, P. C., and Richard, P., The pedestrian/bikeway bridge
of Sherbrooke, in: Proc., 4th International symposium on
‘Utilisation of High Strength/High Performance Concrete’,
Paris, 1996, pp. 1399 – 1406.
12. Behloul, M., and Lee, K. C., Ductal Seonyu footbridge, Structural
Concrete, Vol. 4, 203, Telford, London, pp. 195 – 201.
13. Perry, V. H., Case studies on innovative applications and
challenges of introducing breakthrough technologies (UHPC)
in the construction industry, in: Ref.10, pp. 33 – 41.
14. Naaman, A. E., Development and Evolution of Tensile
Strain-hardening FRC Composites, Proceedings, Seventh
International RILEM Symposium on Fibre Reinforced
Concrete: Design and Applications, (BEFIB 2008), Chennai,
September, pp.1 – 28.
15. Denarie, E., and Bruhwiler, E., Structural Rehabilitations
with Ultra High Performance Fibre Reinforced Concretes,
International Journal for Restoration of Buildings and
Monuments, Aedificatio, Vol. 12, No. 5 and 6, 2006,
pp. 453 – 467.
16. Viswanathan, T., and Mullick, A. K., Design and construction
of Link slabs for jointless bridge decks with high performance
fibre reinforced concrete (HPFRC), Highway Research
Journal, Highway Research Board, Indian Roads Congress,
New Delhi, Vol. 4, No. 2, July – December 2011, pp.25 – 40.

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